The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The invention relates generally to the exploitation of hydrocarbon-containing formations. More specifically, the invention relates to methods and fluids for scale inhibition and/or squeeze treatments that are used to optimize and/or enhance the production of hydrocarbon from a formation.
Hydrocarbons (oil, natural gas, etc.) are typically obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation. In order for hydrocarbons to be “produced,” that is, travel from the formation to the wellbore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the wellbore. This flowpath is through the formation rock, e.g., solid carbonates or sandstones having pores of sufficient size, connectivity, and number to provide a conduit for the hydrocarbon to move through the formation.
Recovery of hydrocarbons from a subterranean formation is known as “production.” During production, water containing a number of dissolved salts is often coproduced with the hydrocarbon. Especially when the formation is a carbonate, calcium cations are prevalent, as are carbonate and phosphate anions. The combination products of calcium cation with carbonate anion or phosphate anion can precipitate from the water in which the ions are carried to form “scale” deposits when the concentrations of these anions and cations exceed the solubility of the reaction product. The formation of scale in either the wellbore or reservoir or both can slow oil production rate and, in extreme circumstances, stop production completely.
Also, produced water is an inevitable consequence of water injection when water flooding is used to develop an oil reservoir, and scale can slow oil production rate. One typical method of preventing scale deposits forming is to inject or ‘squeeze’ a scale inhibitor into the reservoir rock where it adsorbs onto the reservoir rock surfaces and helps prevent or diminish scale deposition. The scale inhibitor desorbs in the water phase during oil production until it reaches a certain critical level (minimum inhibitor concentration) when a further squeeze treatment is required.
However, a problem that limits the effectiveness of scale inhibitor treatments is ensuring that the scale inhibitor is delivered to the desired zone. This is particularly a challenge in long, open hole horizontal well bores where heterogeneity in permeability occurs and/or water production is high. It would be difficult for injection of scale inhibitor made in a single stage to reach the far end of a horizontal wellbore penetrating the formation. When there is permeability contrast between zones or a water-producing zone the initially injected scale inhibitor may tend to enter the most permeable layer first leaving other parts of the wellbore untreated. The untreated zones may also be producing water and require protection from the scale inhibitor.
Hence, desired are diversion fluids that can prevent scale forming and be placed over the whole length of the desired zones improving zonal coverage, which generate viscosity and are compatible with scale inhibitors. In addition, what is desired are fluids which decrease in viscosity prior to or during production of the well to prevent the gel blocking the pores of the reservoir rock and lowering oil production. Fluids which provide such advantages are provided, at least in part, by the following invention.